This invention relates to a reciprocating pump. More particularly, the present invention relates to a reciprocating pump suited to be used as a pump for feeding gasoline to a gasoline engine.
Heretofore, a radial piston pump, a swash plate type pump, etc. have been known as a pump of this type. Those reciprocating pumps are designed such that by reciprocally moving a plunger (the term "plunger" in this invention includes a piston) provided in a cylinder bore of a cylinder member, oil is introduced into a pressure chamber and the oil thus introduced is pressurized.
In a reciprocating pump, a gap for allowing reciprocal strokes of the plunger is formed between an inner peripheral surface of the cylinder bore and an outer peripheral surface of the plunger. For this reason, there is an inconvenience that oil pressurized in the pressure chamber partly leaks outside from an opening portion of the cylinder bore through this gap. Especially, in case the oil to be pressurized is gasoline, lubricant, such as grease, to be applied to a rotating portion or sliding portion of the reciprocating pump is diluted by the gasoline leaked into the casing of the pump from the cylinder bore. As a result, there is a fear that seizing or the like will occur to the rotating portion or sliding portion.
To overcome this inconvenience, Japanese Utility Model Laid-Open Publication No. 43274/1994 discloses a reciprocating pump, in which a film (sealing member) expansible and contractible in response to reciprocal stroke of a plunger is provided between the cylinder member and the plunger such that the opening portion of the cylinder bore can be covered with the film, thereby defining a hermetically closed space by the cylinder member, the plunger and the film. Then, by receiving the gasoline leaked between the inner peripheral surface of the cylinder bore and the outer peripheral surface of the plunger into the hermetically closed space, the gasoline is prevented from leaking into the casing.
It should be noted here that if the above space is completely closed with respect to outside, the completely closed space is filled with the gasoline leaked and as a result, the film is ruptured or becomes unable to expand or contract. To overcome this inconvenience, in the pump disclosed in the above-mentioned Publication, the hermetically closed space is connected to a tank so that the gasoline leaked into the space can be returned to the tank.
However, for returning the gasoline to the tank, it becomes necessary to newly provide a piping between the casing and the tank. Therefore, the installing cost is increased to that extent. Moreover, much time and labor is required for piping operation. In addition, extra installation space is required for the piping.